Offset object duplicated along path
I tried to obtain what you describe: it wasn't extremely simple, but I think the result should be something near, at least:



How it is done? 


added the path
added a 5 vertex segment
added a curve modifier to the segment (highlighted in the above image), targeting the curve, along X
now moving the segment along X (animating with loc keyframes) it follows the curve
then added 5 spheres, each snapped to each of the segment vertices, then each vertex parented to the segment
alternatively, and more efficiently, you can parent one sphere to the segment, then select the segment and enable duplication on "verts".


the following images show the alternative method, and also a movement along a more complicated curve:





there are probably other ways, but this should be near.